1. Field of the Invention
The present invention relates to magnetic bearing suspensions for relatively rotatable elements.
2. Description of the Prior Art
Magnetic bearing suspensions have been devised using various configurations of permanent magnets and electromagnets to provide stable suspension of rotating shafts or other devices, see, for example, "A Magnetic Journal Bearing", by F. T. Backers, Phillips Technical Review, Vol. 22, No. 7, 1960/61. Such a device comprises a plurality of permanent magnet discs which are radially polarized, thereby resulting in problems due to its radial repulsion design. First, the radially magnetized rings are very difficult to manufacture, especially in small sizes required for weight-effective designs. Second, local nonuniformity of magnetic strength produces flux variations and resulting eddy current and hysteresis losses when the suspended shaft is rotated, thereby resulting in large undesirable "friction" drag torques.
Another system utilizing axial attraction is disclosed in U.S. Pat. No. 23 2,340,122 to Hansen, Jr. That patent describes a magnetic bearing utilizing iron pole pieces of triangular cross-section, placed between axially polarized permanent magnets, thereby providing an arrangement for an axial attraction magnetic bearing. Such a bearing is radially unstable because poles of opposite polarity are adjacent the two members. The triangularity of the iron pole pieces are used to assist in turning and in the concentration of the fluxes and the iron poles are magnetically saturated to avoid an undesirable tangential path for fluxes.